Direct Detection of Herceptin/Trastuzumab Binding on Breast Tissue Sections

Alexey Glazyrin ¹, Xiaoyun Shen ¹, Victoria Blanc ¹ and James F. Eliason ^1*

¹ Asterand, PLC, Detroit, Michigan

^* To whom correspondence should be addressed. E-mail: jeliason{at}asterand.com .

Submitted on May 11, 2006
Accepted on 5 August 2006

	Abstract

The proto-oncogene product HER-2/neu is the target of the humanized monoclonal antibody trastuzumab (Herceptin). Several tests are used clinically to identify patients with HER-2/neu overexpression based on evaluation by pathologists of gene amplification by fluorescence in situ hybridization (FISH) or protein expression using immunohistochemistry (IHC). A simple technique has been developed for staining formalin-fixed, paraffin embedded breast cancer tissue using unmodified Herceptin/trastuzumab as the primary antibody. Results were compared with staining with the commercial kit, HercepTest, as well as with polyclonal anti-HER-2/neu antibodies and with biotinylated trastuzumab. These procedures were tested using 4 breast cancer microarrays. There were 854 cores that were stained with all 4 antibodies, representing 325 cases. A standard 4 point scoring system (0-3) was used. A total of 156 of the cases (48%) were scored as 0 by all the methods used and 31 (9.5%) were negative by all methods. Of interest, 3 cases were scored negative using polyclonal anti-HER-2/neu antibodies, but were positive using unmodified trastuzumab. To clarify this discrepancy, whole sections of tumors were examined with both antibodies using double labeling. There were some tumors that demonstrated a mosaic pattern of staining with neighboring cells or groups of cells stained exclusively with one antibody or the other. These results demonstrate that unmodified humanized or human therapeutic antibodies could be used for preclinical testing or in a clinical laboratory setting for IHC based selection of patients for treatment and results of such selection could be different from those obtained using polyclonal antibodies based IHC procedure.

Key Words: HER-2/neu, theranostics, immunohistochemistry, trastuzumab, Herceptin

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